The invention relates to a method and apparatus for performing an automatic power adjustment for an optical signal and in particular of an optical signal within a wavelength division multiplexing WDM optical network.
In wavelength division multiplexing WDM networks, multiple optical carrier signals are multiplexed on a single optical fiber by using different wavelengths (also called colours) of laser light to carry different signals. This increases data transmission capacity and enables bi-directional communication over the same strand of optical fibers. In wavelength divisional multiplexing optical networks, in particular in dense wavelength division multiplexing DWDM optical networks, it is desirable to attain a flat optical spectrum at the egress of each node of the network across all wavelengths. When a wavelength divisional multiplexing (WDM) optical network comprises fixed optical add/drop multiplexing (FOADM) nodes, balancing of optical powers for all wavelengths can be challenging. These FOADM nodes comprise fixed OADM filters that provide no power adjustment for power balancing. However, the transmitted optical power levels for the transponders and muxponders installed in such FOADM nodes can vary up to 10 dB, i.e. the transmit powers can vary from e.g. −3 dB to +7 dB. These power variations can be further increased by the different loss of the different filters used by the wavelengths on the multiplexing path.
Accordingly, in conventional wavelength divisional multiplexing (WDM) optical networks, balancing the optical spectrum for an optical add/drop multiplexing node typically requires a manual power adjustment by a user using fixed in-line signal attenuators and power measuring devices such as power meters and/or spectrum analyzers. This procedure of manual balancing the optical power levels is very cumbersome and time consuming and affects all users of the optical platform including customers, installers, and customer service engineers. Therefore, there is a need to provide a more manageable solution for balancing the optical power levels which avoid a manual power adjustment to balance the optical spectrum at an optical add/drop multiplexing node of an optical network.